1. Field of the Invention
This invention relates to a method of reproducing a radiation image in a radiation image recording and reproducing system using a stimulable phosphor sheet, and an apparatus for carrying out the method.
2. Description of the Prior Art
When certain kinds of phosphors are exposed to a radiation such as X-rays, .alpha.-rays, .beta.-rays, .gamma.-rays, cathode rays or ultraviolet rays, they store a part of the energy of the radiation. Then, when the phosphor which has been exposed to the radiation is exposed to stimulating rays such as visible light, light is emitted to the phosphor in proportion to the stored energy of the radiation. A phosphor exhibiting such properties is referred to as a stimulable phosphor.
As disclosed in U.S. Pat. No. 4,258,264 and Japanese Unexamined Patent Publication No. 56(1981)-11395, it has been proposed to use a stimulable phosphor in a radiation image recording and reproducing system. Specifically, a sheet provided with a layer of the stimulable phosphor (hereinafter referred to as a stimulable phosphor sheet) is first exposed to a radiation passing through an object to have a radiation image stored therein, and is then scanned with stimulating rays such as a laser beam which cause it to emit light in the pattern of the stored image. The light emitted by the stimulable phosphor sheet upon stimulation thereof is photoelectrically detected and converted to an electric image signal, which is processed as desired to reproduce a visible image on a recording medium such as a photographic film or on a display device such as a cathode ray tube (CRT).
In the aforesaid radiation image recording and reproducing system, a visible image is reproduced on the basis of the electric image signal obtained by read-out of the radiation image stored in the stimulable phosphor sheet.
However, sensitivity of the stimulable phosphor sheet is not always uniform over the whole surface thereof, and is often different among various portions of the stimulable phosphor sheet. Also, in the image read-out means, light detecting efficiency for the light emitted by the stimulable phosphor sheet is not always uniform over the whole surface of the stimulable phosphor sheet, and is often different among various portions of the stimulable phosphor sheet.
Therefore, the visible image reproduced on the basis of the electric image signal obtained by image readout involves nonuniformity of sensitivity in the stimulable phosphor sheet, the image read-out means or the like.